The present invention relates to a fluid pressure cylinder in which a circular piston and a noncircular rod connected to each other are respectively and movably supported by air bearings in a main body block.
A cylinder system in which a piston and a rod are supported in floating states by air bearings provided to a cylinder block is already known from Japanese Patent Application Laid-open No. 11-117912, for example.
Because the piston and the rod are supported by the air bearings in the proposed cylinder system, sliding resistance of the members can be reduced. However, because outside shapes of both the piston and rod are circular, the members may rotate in their strokes.
However, problems may occur in general if the piston and the rod rotate in operation, there is a desire to prevent rotation of the members in their strokes.
In order to prevent rotation of the piston and the rod, means for preventing rotation may be provided simply. However, if the piston and the rod are supported in the floating states by the air bearings as described above, a mechanism that does not impair functions of supporting in the floating states is necessary. For this purpose, it is easy and proper to form a section of the rod that has a smaller sectional area than the piston into a square or a rectangle. However, it is extremely difficult to integrally form the circular piston and the noncircular rod in a state in which the piston and the rod are kept completely concentric with each other. It is similarly difficult to accurately process the air bearing having a circular bearing surface for supporting the piston and the air bearing having a noncircular bearing surface for supporting the rod such that the bearings are concentric with each other. Therefore, it is extremely difficult to support the above circular piston and noncircular rod concentrically with each other by the air bearings. In order to accurately produce the piston and rod and to stably carry out supporting of the piston and rod in the floating states by the air bearings, an extremely complicated and highly accurate producing process is necessary and it is difficult to easily produce such a fluid pressure cylinder at low cost.
It is a technical object of the present invention to obtain a fluid pressure cylinder which can be produced easily and at low cost and in which a circular piston and a noncircular rod are supported accurately and concentrically with each other respectively by air bearings.
To achieve the above object, according to the present invention, there is provided a fluid pressure cylinder comprising a first air bearing having a circular bearing hole, a second air bearing having a noncircular bearing hole, a circular piston movably housed in the circular bearing hole, and a noncircular rod movably housed in the noncircular bearing hole. The piston and the rod are formed separately as separate parts and the piston and the rod are integrally connected to each other through an adhesive in a state in which the piston is aligned to be concentric with the circular bearing hole of the first air bearing and the rod is aligned to be concentric with the noncircular bearing hole of the second air bearing.
According to the invention with the above structure, because the circular piston and the noncircular rod are bonded to each other in a state in which the piston and the rod are respectively kept concentric with the corresponding air bearings, it is unnecessary to integrally form the piston and the rod in a state in which the piston and the rod are kept concentric with each other. It is similarly unnecessary to accurately process the first air bearing having a circular bearing surface and the second air bearing having a noncircular bearing surface such that the bearings are concentric with each other. Therefore, processing of the respective members is easy and the cylinder can be produced easily at low cost.
According to a concrete embodiment of the invention, the piston has a housing portion for housing the adhesive and a supply hole for supplying the adhesive in the housing portion to junction faces of the piston and the rod.
More concretely, the piston is in a closed-end cylindrical shape having therein a hollow portion that is the housing portion for the adhesive, the piston has the junction face to which the rod is bonded and the supply hole connecting the junction face and the hollow portion at a bottom portion of the piston, and the rod has the junction face to be bonded to the junction face of the piston on an upper end face of the rod.
In the invention, it is preferable that the fluid pressure cylinder has provisionally fixing means for provisionally fixing the piston and the rod to each other for alignment in a non-fixed state.
The provisionally fixing means is formed of a bolt and the bolt is screwed down into the rod in a non-fixed state through the supply hole for the adhesive in the hollow portion in the piston.
It is preferable that a weight of the rod is reduced by providing a plurality of holes for lightening in positions of the rod symmetric with respect to a center of the rod.
The rod may have an air passage for causing fluid pressure or vacuum pressure to act at a tip end portion of the rod.